fix(mnemopi): restore [Unreleased] section after upstream merge

The auto-merge during conflict resolution placed the page-size Added
section under [17.2.3] (which already had the upstream's think-block
fix) and left an empty ### Fixed header. Move the Added section back
under [Unreleased] where it belongs; drop the empty header.

No code changes.

packages/mnemopi/CHANGELOG.md

@@ -2,15 +2,15 @@
 
 ## [Unreleased]
 
+### Added
+
+- Added opt-in SQLite page-size selection for file-backed databases. Set `MNEMOPI_DB_PAGE_SIZE` to a valid SQLite page size (a power of two from 512 to 65536) or `os`, or pass `pageSize` to `openDatabase`. The default remains SQLite's own page size because the virtual-memory page size does not establish storage-block behavior and larger WAL pages can increase sparse-write cost. Existing databases retain their page size.
+
 ## [17.2.3] - 2026-08-01
 
 ### Fixed
 
 - Stripped `<think>…</think>` reasoning blocks from remote LLM output in `cleanOutput`, so reasoning-model responses no longer leak into consolidated memories or corrupt fact extraction (the reasoning wrapper previously survived parsing and every stored fact became reasoning prose). ([#7231](https://github.com/can1357/oh-my-pi/issues/7231))
-### Fixed
-### Added
-
-- Added opt-in SQLite page-size selection for file-backed databases. Set `MNEMOPI_DB_PAGE_SIZE` to a valid SQLite page size (a power of two from 512 to 65536) or `os`, or pass `pageSize` to `openDatabase`. The default remains SQLite's own page size because the virtual-memory page size does not establish storage-block behavior and larger WAL pages can increase sparse-write cost. Existing databases retain their page size.
 
 ## [17.2.2] - 2026-07-31